1. Field of the Invention
The invention relates to a process for preparing organosilanes by hydrosilylation in the presence of an iridium compound as catalyst and free diene as cocatalyst.
2. Background Art
Substituted alkylsilanes are of tremendous economic importance in many fields. They are used, for example, as adhesion promoters and as crosslinkers.
The platinum- or rhodium-catalyzed hydrosilylation of unsaturated compounds has been widely studied in the past. The product yields are often very low, being only 20-45%, which is attributable to considerable secondary reactions.
Iridium catalysts containing diene ligands are, according to U.S. Pat. No. 4,658,050, used in the hydrosilylation of allyl compounds by means of alkoxy-substituted silanes. JP-A-07126271 describes the hydrosilylation of allyl halides using chlorodimethylsilane in the presence of iridium catalysts containing diene ligands. Disadvantages of these processes are either moderate yields, an uneconomically high catalyst concentration and/or a very short catalyst life.
It is an object of the invention to develop a catalyst system which has a long life, which ensures high product yields and purities when using very small amounts of catalyst, and which further allows both continuous and batchwise operation.
The invention provides a process for preparing a silane of the formula I
R6R5CHxe2x80x94R4CHxe2x80x94SiR1R2R3xe2x80x83xe2x80x83(I),
which comprises reacting a silane of the formula II
HSiR1R2R3xe2x80x83xe2x80x83(II),
with an alkene of the formula III
R6R5CHxe2x95x90CHR4xe2x80x83xe2x80x83(III),
in the presence of an iridium compound of the formula IV as catalyst
[(diene)IrCl]2xe2x80x83xe2x80x83(IV),
and free diene as cocatalyst, where
R1, R2, and R3 are each independently a monovalent Sixe2x80x94C-bonded, unsubstituted or halogen-substituted C1-C18-hydrocarbon radical, a chlorine atom or a C1-C18-alkoxy radical,
R4, R5, and R6 are each independently a hydrogen atom, a monovalent C1-C18-hydrocarbon radical which may be unsubstituted or may optionally bear F, Cl, OR, NRxe2x80x22, CN or NCO atoms/groups as substituents, a chlorine atom, a fluorine atom or a C1-C18-alkoxy radical, where in each case 2 radicals R4, R5, R6 together with the carbon atoms to which they are bound may form a cyclic radical,
R is a hydrogen atom or a monovalent C1-C18-hydrocarbon radical and diene is a C4-C50-hydrocarbon compound which may be unsubstituted or bear F, Cl, OR, NRxe2x80x22, CN or NCO atoms/groups as substituents and has at least two ethylenic Cxe2x95x90C double bonds.
In this process, the target products of the formula I are typically obtained in yields of from 95% to 98% when using very small amounts of catalyst. Depending on the field of application, work-up by distillation can therefore often be dispensed with.
C1-C18-hydrocarbon radicals R1, R2, R3 are preferably alkyl, alkenyl, cycloalkyl or aryl radicals. R1, R2, R3 preferably have not more than 10, in particular not more than 6, carbon atoms. R1, R2, R3 are preferably linear or branched C1-C6-alkyl radicals or C1-C6-alkoxy radicals. Preferred halogen substituents are fluorine and chlorine. Particularly preferred radicals R1, R2, R3 are methyl, ethyl, methoxy, ethoxy, chlorine, phenyl and vinyl.
Hydrocarbon radicals R4, R5, R6 are preferably alkyl, alkenyl, cycloalkyl or aryl radicals. It is preferred that not more than one of R4, R5, R6 is an alkoxy radical. R5, R6 preferably have not more than 10, in particular not more than 6, carbon atoms. R5, R6 are preferably linear or branched C1-C6-alkyl radicals or C1-C6-alkoxy radicals. Particularly preferred radicals R5, R6 are hydrogen, methyl, ethyl, chlorine and phenyl.
The hydrocarbon radical R4 preferably has not more than 6, in particular not more than 2, carbon atoms. Particularly preferred radicals R4 are hydrogen, methyl, and ethyl.
The hydrocarbon radical R preferably has not more than 6, in particular not more than 2, carbon atoms.
The hydrocarbon compounds used as diene may comprise not only molecular units containing the ethylenic Cxe2x95x90C double bonds, but may also comprise alkyl, cycloalkyl or aryl units. The dienes preferably have from 6 to 12 carbon atoms. Preference is given to monocyclic or bicyclic dienes. Preferred examples of dienes are butadiene, 1,3-hexadiene, 1,4-hexadiene, 1,5-hexadiene, isoprene, 1,3-cyclohexadiene, 1,3-cyclooctadiene, 1,4-cyclooctadiene, 1,5-cyclooctadiene and norbornadiene.
The diene in the catalyst of the formula IV and the free diene serving as cocatalyst can be identical or different. Preference is given to the two dienes being identical.
In a particularly preferred case, the catalyst of the formula IV used is [(cycloocta-1c,5c-diene)IrCl]2 and the cocatalyst used is 1,5-cyclooctadiene.
The silane component of the formula II is preferably used in an excess of from 0.01 to 100 mol % of II, more preferably from 0.1 to 10 mol %, based on the alkene of the formula III. The iridium compound of the formula IV is preferably present in a concentration of from 5 to 250 ppm, in particular from 10 to 50 ppm, based on all components present in the reaction mixture. The diene as cocatalyst is preferably added in a concentration of from 50 to 2500 ppm, in particular from 50 to 1000 ppm, based on all components present in the reaction mixture.
The process can be carried out in the presence or absence of aprotic solvents. If aprotic solvents are used, solvents or solvent mixtures having a boiling point or boiling range up to 120xc2x0 C. at 0.1 MPa are preferred. Examples of such solvents are ethers such as dioxane, tetrahydrofuran, diethyl ether, diisopropyl ether, and diethylene glycol dimethyl ether; chlorinated hydrocarbons such as dichloromethane, trichloromethane, tetrachloromethane, 1,2-dichloroethane, and trichloroethylene; hydrocarbons such as pentane, n-hexane, hexane isomer mixtures, heptane, octane, naphtha, petroleum ether, benzene, toluene, and xylene(s); ketones such as acetone, methyl ethyl ketone, diisopropyl ketone, and methyl isobutyl ketone (MIBK); esters such as ethyl acetate, butyl acetate, propyl propionate, ethyl butyrate, and ethyl isobutyrate; carbon disulfide; and nitrobenzene, or mixtures of these solvents. This list is exemplary and not limiting.
The target product of the formula I can also be used as an aprotic solvent in the process. This process variant is preferred. For example, the reaction components of the formula II together with the iridium catalyst of the formula IV and optionally the diene are placed in a reaction vessel and the reaction component of the formula III, optionally in admixture with the diene, is introduced while stirring. In another variant, the target product of the formula I together with the catalyst of the formula IV and optionally diene are placed in a reaction vessel and a mixture of components II, III and optionally diene is introduced. The reaction time to be employed is preferably from 10 to 2000 minutes. The reaction is preferably carried out at a temperature of from 0 to 300xc2x0 C., in particular from 20 to 200xc2x0 C. The use of superatmospheric pressure may also be useful; the pressure is preferably up to 100 bar.
The addition of the diene also allows a plurality of reactions to be carried out without further addition of catalyst. Preference is given to adding further amounts of diene as cocatalyst as the reaction proceeds, in particular, in a continuous manner.
The meanings of all the symbols in the formulae above are in each case independent of one another. In the following examples, all concentrations and percentages are by weight, all pressures are 0.10 MPa (abs.) and all temperatures are 20xc2x0 C. unless indicated otherwise.